Proceedings of The Physiological Society

University College Cork (2004) J Physiol 560P, C14

Communications

THE CARDIOVASCULAR RESPONSE TO HUMAN CALF MUSCLE STRETCH IS INDEPENDENT OF THE LEVEL OF CONCURRENT MUSCLE METABOREFLEX STIMULATION

Fisher,James P.; Bell,Martin P.D.; White,Michael J.;

1. School of Sport and Exercise Sciences, University of Birmingham, Birmingham, United Kingdom.


The cardiovascular response to external calf muscle compression, believed to stimulate muscle mechanoreceptors, is progressively augmented by increasing levels of muscle metaboreflex stimulation during post exercise circulatory occlusion (PECO) (White & Bell, 2003}. The cardiovascular response to muscle mechanoreceptor stimulation by passive stretch of calf muscles (STRETCH) differs from that of external compression (Gladwell & Coote, 2002). However, the interaction between STRETCH and muscle metaboreflex activation is unknown. To examine this interaction eight (7 male) active young (22 ±1yr) subjects were recruited. With local ethics committe approval subjects were seated semi-supine in a Biodex System 3 with the right knee flexed at 150 degrees and the foot attached to the ankle attachment. Heart rate and blood pressure was measured using ECG and Finapres. Phase of respiratory cycle was detected by a strain gauge placed around the chest. Following 115s of rest a cuff was inflated around the right thigh to 200mmHg. Subjects then performed 90s of isometric calf plantarflexion at either 0, 30, 50 and 70% of maximum voluntary contraction (MVC). With the thigh cuff still inflated subjects rested for 90s (the last 60s of period taken as PECO1), then the Biodex moved the foot to full dorsiflexion where it was held for 60s of STRETCH. After a further 60s of rest (PECO2) the thigh cuff was deflated. Subjects performed 2 trials at each exercise intensity and breathed to a metronome at their eupnoeic frequency. Statistical analysis was performed using MANOVA and repeated measures ANOVA, with significance taken as P<0.05. During PECO1 and PECO2 blood pressure was progressively elevated above baseline following the 0-70% MVC trials (p<0.05). Figure 1 shows that STRETCH produced a further significant (p<0.05) blood pressure rise, the magnitude of which was not significantly different between trials. HR increased to the same extent during the first 3 cardiac cycles of the STRETCH period in all trials. However it recovered rapidly, such that overall there was no significant elevation above baseline during STRETCH. We conclude that the cardiovascular response to calf muscle stretch is unaffected by the level of muscle metaboreflex stimulation in that same muscle group, suggesting that the stretch activated muscle mechanoreflex is not sensitised by the metabolic conditions within the muscle. This is in contrast to the cardiovascular responses to muscle compression, which appear to be augmented when the metabolic conditions within the muscle are elevated. Figure 1.

Where applicable, experiments conform with Society ethical requirements